This proposal concerns the use of beclomethasone dipropionate (BDP) as a post-exposure drug therapy having the potential to mitigate the gastrointestinal (GI) injury associated with acute radiation syndrome (ARS) following exposure to intense ionizing radiation. ARS occurs after toxic radiation exposure and involves at least several organ systems, primarily resulting in toxicity to the bone marrow (hematopoietic [HP] syndrome) and the GI (GI-ARS). In the event of a nuclear disaster or terrorist detonation of a nuclear bomb, casualties exposed to >2 Gray (Gy) are at high risk for development of clinically significant ARS. Exposure to high doses of radiation exceeding 10-12 Gy causes acute gastrointestinal injury which can result in death in 5-10 days. Thus, the extent of injury to the bone marrow and the GI tract are the principal determinants of survival after exposure to total- body irradiation (TBI). Although lethal hematopoietic injury can be rescued by bone marrow transplantation and several therapeutic drugs, there is no treatment or preventive measure for GI damage that occurs after high dose radiation. We evaluated an oral formulation of beclomethasone dipropionate (BDP), a mucosally active glucocorticoid, as a treatment of dogs to mitigate acute GI syndrome. The primary result that justifies further study of this drug in the GI-ARS is the survival benefit in dogs that have received BDP therapy starting 2 hours following lethal TBI. Preliminary results also suggest BDP efficacy starting at 24 hours after TBI. With this application, we are proposing further evaluation of the oral drug in beagle dogs with a focus on intervention at least 24 hours after TBI. The dog is one of the crucial large animal models that will aid in establishing efficacy of BDP (or other drugs) for eventual FDA licensure under the Animal Rule. We envision future studies that would occur in mouse models on refinement of the putative mechanisms of BDP in GI-ARS, as wells as studies of orally administered BDP in non-human primates.